EvalDLL evaluation on Windows

The EvalDll library on Windows is provided both as C++ and C# library. A NuGet package is also available at nuget.org. Please note that Visual Studio 2015 Update 3 is required and the target platform in the project property should be X64.

Using the EvalDll library

The EvalDll library enables programmatic model evaluation on CPU (GPU is not supported).
The usage pattern for this DLL is the following:

  1. Link the Cntk.Eval-<VERSION>.lib import library into the application. Ensure you use the correct file name - see the beginning of this article.
  2. Include the evaluation header file "Eval.h"
  3. Get an instance of the evaluation engine specific for the model's data type (float or double).
  4. Load the model (or create the network) in the evaluation engine.
  5. Evaluate some input against the model and obtain the corresponding output.
  6. Dispose the model when done.

For details on the C++ API provided by EvalDll, please refer to the EvalDll C++ API page.

The CPPEvalClient program located in the folder Examples/Evaluation/LegacyEvalDll/CPPEvalClient demonstrates the usage of this evaluation interface. Please see the EvalDll Examples page for how to build and run examples.

Using the EvalDll C# library

CNTK provides a managed (.Net) library wrapper named Cntk.Eval.Wrapper. This library wraps the native EvalDll library and exposes a managed interface. This interface provides the same functionality as the native interface, with the addition of some convenience methods. Alike its native counterpart, this library can only perform evaluations using the CPU (no GPU used). The library is written in CLI/C++ and thus forms the bridge between .Net (e.g. C#) and the native C++ side.

For details regarding the managed API provided by EvalWrapper.DLL, refer to the EvalDll Managed API page.

The usage pattern for the managed wrapper is simple:

using Microsoft.MSR.CNTK.Extensibility.Managed;
    using (var model = new IEvaluateModelManagedF())
        // Load model
catch (CNTKException ex)
catch (Exception ex)

There are several examples of performing a programmatic CNTK model evaluation in C# inside the CSEvalClient project. Please see the EvalDll Examples page for how to build and run examples.

NuGet Package

There is currently a NuGet package at nuget.org (search for CNTK) that provides both the native and managed versions for Debug and Release for the CNTK evaluation libraries (CPU only using MKL). With the NuGet it is possible to simply add the CNTK Eval NuGet to a .Net or Win32 project and call the APIs. Please refer to the NuGet Package page for details on how to get started with CNTK and NuGet.

If you do not want to use NuGet Package, you can add Cntk.Eval.Wrapper-<VERSION>.dll as reference to your project. Please make sure in this case that the path to the Cntk.Eval.Wrapper DLL and its dependencies below are included in the search path of DLLs for your application.

Shipping EvalDll Library with your Windows application

EvalDll requires the Visual C++ Redistributable Package for Visual Studio 2015 to be installed on the system where your application is going to run. And the target platform in the project property should be X64.

This page describes how CNTK binary files are named.

If you own application uses EvalDll library you need to distribute these DLLs with your application:

  • Cntk.Eval-<VERSION>.dll
  • Cntk.Eval.Wrapper-<VERSION>.dll
  • Cntk.Math-<VERSION>.dll
  • libiomp5md.dll
  • mklml.dll

All these DLLs can be found in the CNTK binary release version, see the CNTK Releases page.